The 3GPP initiative “License Assisted Access” (LAA) intends to allow LTE equipment to also operate in the unlicensed 5 GHz radio spectrum. The unlicensed 5 GHz spectrum is used as a complement to the licensed spectrum. Accordingly, devices connect in the licensed spectrum (primary cell or PCell) and use carrier aggregation to benefit from additional transmission capacity in the unlicensed spectrum (secondary cell or SCell). To reduce the changes required for aggregating licensed and unlicensed spectrum, the LTE frame timing in the primary cell is simultaneously used in the secondary cell.
Regulatory requirements, however, may not permit transmissions in the unlicensed spectrum without prior channel sensing. Since the unlicensed spectrum must be shared with other radios of similar or dissimilar wireless technologies, a so called listen-before-talk (LBT) method may need to be applied. Today, the unlicensed 5 GHz spectrum is mainly used by equipment implementing the IEEE 802.11 Wireless Local Area Network (WLAN) standard. This standard is known under its marketing brand “Wi-Fi.”
In dense Wi-Fi deployments the number of APs (Access Points) can exceed the number of available unlicensed channels, forcing multiple APs to operate on the same channels. A typical example of prior art for channel selection in Wi-Fi is “LAC: Load-aware channel selection in 802.11 WLANs,” Proc. IEEE PIMRC, 2008. LAC is a distributed channel allocation method where multiple APs exchange interference and contention measurements of their associated clients and iteratively derive the optimal channel allocation. In another example of prior art, “Measurement-based self organization of interfering 802.11 wireless access networks,” Proc. IEEE INFOCOM, 2007, each AP measures the total received power from all neighbor APs for every channel and selects a channel with a reduced/minimum total power. This is performed at each AP by measuring the RSSI (Received Signal Strength Indicator) of the received beacon frames from all neighboring APs at every channel. However, this method may not take into account the number of associated clients of an AP.
In Rel-13 LAA, carrier selection and dynamic frequency selection (DFS) may be required functionalities for several regions and bands. The carrier selection process may be separate and on a slower time scale compared to the LBT/CCA (Listen Before Talk/Clear Channel Assessment) procedure prior to transmissions on the unlicensed channels.
There is currently no carrier selection specification or associated signaling specified for LTE. So far, LTE has operated exclusively in licensed spectrum. Increasing/Optimizing the carrier or channel selection mechanism for the LAA SCells may lead to improved coexistence and spectrum sharing with Wi-Fi and other unlicensed devices. From a specification perspective, new signaling in LTE may be required to enable coordinated carrier selection.
The approaches described in the Background section could be pursued, but are not necessarily approaches that have been previously conceived or pursued. Therefore, unless otherwise indicated herein, the approaches described in the Background section are not prior to the claims in this application and are not admitted to be prior art by inclusion in the Background section.